Pitch circle diameter is a term used to describe the centerline diameter of a circular bolt spacing, the diameter of theoretical friction discs that would transmit the same velocity ratio as two meshing gears, or the diameter at which the thread tooth equals the thread spacing for screw threads. Context should be used to determine whether the term is being used to describe bolt spacing, gears or threads.Continue Reading
For bolt or screw spacing, pitch circle diameter or PCD, also called the bolt circle diameter or BDC, is the diameter of an imaginary circle passing through the center of bolts distributed around a component such as a wheel, hub or housing. Once the pitch circle diameter is established, one need only specify the number of holes or threads and dimensions of each hole or thread to describe the full bolt pattern.
For two meshing gears, the pitch circle diameter represents each of two imaginary friction discs that, when spun together without slippage, would result in the identical velocity ratio and gear ratio as the actual gears. The pitch circle diameter is thus an important geometrical term for engineers in describing the mechanical relationship of a gear set.
To accurately measure the pitch circle diameter or pitch diameter of a thread requires either an optical comparator measuring device or thread wires.Learn more about Measurements
An American National standard taper pipe thread chart includes the nominal pipe size, outside diameter, threads per inch and the pitch of the thread. The chart on the Machining Products website also includes measures of the length and diameter for hand tight engagement, effective external thread, wrench makeup length of the internal thread and nominal perfect external thread.Full Answer >
The National Pipe Straight Mechanical thread chart provides the thread allowance, major diameter and pitch diameter of the external thread, as well as the minor diameter and pitch diameter of the internal thread for each of the nominal pipe size. It also lists the threads per inch.Full Answer >
An Acme screw thread is a type of screw featuring trapezoidal threads, a height half their pitch and an included angle of 29 degrees. They are made in several varieties and are often used in industrial applications requiring heavy torque and power transmission such as lathes, milling machines and presses.Full Answer >
Thread pitch standards are standard values for pitches of different screw thread sizes. A screw thread's pitch is the distance from one of the thread's ridges to the next equal ridge. Thread pitch standards are distinct from pitch diameter standards, which measure the distance from the center of the screw to its pitch line. Thread pitch standards are measured in threads per inch, while pitch diameter standards use inches.Full Answer >